title: Influence of ambient temperature and minute ventilation on passive and active heat and moisture exchangers.
abstract: OBJECTIVE
  During invasive mechanical ventilation, inspired gases must be humidified. We previously showed that high ambient temperature greatly impaired the hygrometric performance of heated wire-heated humidifiers. The aim of this bench and clinical study was to assess the humidification performance of passive and active heat and moisture exchangers (HMEs) and the impact of ambient temperature and ventilator settings.
  
  
  METHODS
  We first tested on the bench a device with passive and active humidification properties (Humid-Heat, Teleflex), and 2 passive hydrophobic/hygroscopic HMEs (Hygrobac and Hygrobac S, Tyco Healthcare). The devices were tested at 3 different ambient temperatures (from 22 to 30 °C), and at 2 minute ventilation settings (10 and 20 L/min). Inspired gas hygrometry was measured at the Y-piece with the psychrometric method. In addition to the bench study, we measured the hygrometry of inspired gases in 2 different clinical studies. In 15 mechanically ventilated patients, we evaluated Humid-Heat at different settings. Additionally, we evaluated Humid-Heat and compared it with Hygrobac in a crossover study in 10 patients.
  
  
  RESULTS
  On the bench, with the Hygrobac and Hygrobac S the inspired absolute humidity was ∼ 30 mg H2O/L, and with the Humid-Heat, slightly < 35 mg H2O/L. Ambient temperature and minute ventilation did not have a clinically important difference on the performance of the tested devices. During the clinical evaluation, Humid-Heat provided inspired humidity in a range from 28.5 to 42.0 mg H2O/L, depending on settings, and was only weakly influenced by the patient's body temperature.
  
  
  CONCLUSIONS
  In this study both passive and active HMEs had stable humidification performance with negligible influence of ambient temperature and minute ventilation. This contrasts with previous findings with heated wire-heated humidifiers. Although there are no clear data demonstrating that higher humidification impacts outcomes, it is worth noting that humidity was significantly higher with the active HME.
authors.affiliation: Service de Réanimation Médicale, AP-HP, Centre Hospitalier Albert Chenevier, Hôpitaux Universitaires Henri Mondor, Créteil, France.
authors.forename: François
authors.initials: F
authors.lastname: Lellouche
authors.forename: Siham
authors.initials: S
authors.lastname: Qader
authors.forename: Solenne
authors.initials: S
authors.lastname: Taillé
authors.forename: Aissam
authors.initials: A
authors.lastname: Lyazidi
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
mesh_terms: D018592:Cross-Over Studies; D006801:Humans; D006813:Humidity; D001239:Inhalation; D012123:Pulmonary Ventilation; D012121:Respiration, Artificial / Q000295:instrumentation*; D013696:Temperature; D012122:Ventilators, Mechanical
keywords: Mechanical ventilation; critically ill patients; heat and moisture exchangers; humidification